Hydraulic actuator and control unit



M.C.BOKELMAN HYDRAULIC ACTUATOR AND CONTROL UNIT Nov. 24, 1964 3 Sheets-Sheet l Filed Deo. 28, 1961 M Off@- Nov. 24, 1964 M C, BOKELMAN 3,158,068

HYDRAULIC ACTUATOR AND CONTROL UNIT Filed Dec. 28, 1961 3 Sheets-Sheet 2 Nov. Y24, 1964 M. c. BoKx-:LMAN f 3,158,058

HYDRAULIC ACTUATOR AND CONTROL. UNIT fg@ f Q9 .15a-M62M13 United States Patent O 3,158,065 YTJBRUIJIS ACUATR Alt-) CNTRGL TUNE This invention relates to hydraulicr actuators and particularly those capable of eiecting reciprocatory move- Vments and including control devices formed therewith effective to control the direction and extent of reciprocation within the limits of movement or the device and also eiective at all times to lock the actuator component against movement except as so far as movement is permitted by the control means.

An object of the invention is to provide a hydraulic actuator and control means therefor in which the device is characterized by light weight and compact construction particularly adapting it for use in the control of aircraft components.

Another object of the invention is to provide a hydraulic actuator and control means in a unit which is capable upon either complete or partial failure of the source of operating pressure of retaining the operative integrity of its position locking characteristics.

Still another obejct of the invention is to provide a device of the above character in which the fluid controlling valve means and the actuator cylinder is formed in a unitary body construction characterized by compact arrangement of fluid passages therewithin with resultant achievement of small size and light weight in the completed device.

With the foregoing objects in view together with such objects and advantages as may subsequently appear, the invention resides in the parts, and in the construction, combination and arrangement of parts described, by way of example in the following specification of a presently preferred embodiment of the invention, reference being had to the accompanying drawings which form a part of said speciiication and in which drawings:

FIG. 1 is a side elevational view of a combined hydraulic actuator and control means embodying the present invention,

FIG. 2 is an end elevational view as viewed from the lett hand end of FIG. 1,

FIG. 3 is a partially sectional end elevational view taken on the line 3 3 of FIG. l,

FIG. 4 is an enlarged scale, medial longitudinal sectional view taken on the line 4 4 of FIG. 2,

FIG. 5 is a fragmentary view showing details or" the motion limiting means for the control element of the device,

FIG. 6 is a transverse sectional view taken on the line 6 6 of FIG. 4,

FIG. 7 is a fragmentary sectional view taken on the line 7 7 of FIG. 2,

FIG. 8 is a fragmentary sectional view taken on the line 3 8 of FIG. 2,

FIGS. 9, 1t), Il and 12 are, respectively, transverse sectional views taken on the lines 9 9, N I, Il lll and 1?; 12 of FIG. 4.

FIG. i3 is a fragmentary sectional view taken on the line 13 13 of FIG. 3,

FIG. 14 is a schematic diagram showing the device with the control means in its neutral positon,

FIG. 15 is a schematic view similar to FIG. 14 but showing the control means displaced to eifect or to permit movement of the actuator to the right as viewed in that iigure, and

FIG. 16 is a third diagrammatic view similar to the .gigde .imatented Nov. 24, lgtid ICC preceding views but showing the control means moved to effect or to permit movement of the actuator to the left as viewed in that figure.

Referring to the drawings the illustrated embodiment of the invention comprises a base member 1 having a cylinder bore 2 formed therein, said bore accommodating a piston 3 formed as an integral part of a hollow cylindrical piston rod 4 guided for reciprocation in a stuing box portion 6 constituting a reduced diameter bore at one end of the cylinder, said reduced diameter bore being interrupted by a peripheral groove containing a gasket 8 supported by a backing ring 8 and at its outer end having a scraper ring 9 supported by ya washer 1G secured therein by a snap ring II. Externally of the bearing bore 5, the piston rod is provided with a reduced diameter internally threaded portion 12 engaging the shank 13 of an eye bolt 14 attachable to an element of mechanism E to which further reference will hereinafter be made.

The piston rod 4 extends beyond the piston 3 and is guided in a bearing portion 15 is a stufting box member I6 which is externally threaded and which engages an internally threaded enlarged diameter end portion 17 of the cylinder 2. Inwardly of the threaded portion thereof, the stuing box member 16 is provided with a cylindrical end portion 18 having a peripheral groove housing a gasket I9 to prevent iuid leakage from the cylinder. The stuiiing box member 16 is provided with a peripheral grove housing a gasket 2@ supported by a back-up ring 20 which engages the piston 4 to prevent leakage at that point. The piston 3 is provided with a deep peripheral groove in which is seated piston ring meams ZI engaging the cylinder wall.

The threaded portion of the stuing box member 16 extends outside of the end of the member 1 and carries a lock nut 22 etective to lock it in position. The stuiing box member I6 beyond the piston rod bearing portion thereof surrounding the piston rod is slightly enlarged in diameter so as not to contact the piston rod and extends beyond the piston rod for a distance permitting the full traverse of the cylinder and piston, the piston rod thus being protected against the entrance of dust orV other deieterious substances. The stuiiing box member I6 terminates at its distal end in a yoke member 23 and attachable to an element of mechanism E at the bottom of the yoke the end wall of the stuing box member is provided with a breather hole Z4 to accommodate the volumetric pressures therewithin occasioned by relative movelment of the cylinder and piston.

The body ll is provided with a controlling valve bore 25 disposed parallel `and adjacent to the cylinder bore 2 said bore at the end thereof adjacent the stufling box member I6 terminating in a shallow counterbore 26 closed by an end cap 2'7 held in place therein lby a snap ring 28. Adjacent its other end, the bore 25 is provided with a counterbore portion 2% which leads into an internally threaded portion 3@ leading to the exterior of the member 1. Seated in the bore 25 attachable to an element of mechanism E and extending from the counterbore 29 to a point adjacent to the counterbore 26 is a cylindrical valve guide member 31 having a flange 32 engaging the bottom of the counterbore 29 and being seated on said counterbore and in the bore 25 by a nut 33 engaging the threads 30, said nut having an axial bore 34 extending therethrough for reception of an operating link member 35 presently to be described in more detail. The exterior surface of the valve guide member 31 is provided with a spaced series of peripheral grooves housing gaskets 36, 37, 33, 39, 4t) and L-ii reading from left to right as shown in FIG. 4, said gaskets engaging the bore 25 and preventing fluid leakage in the space between the exterior of the Valve guide member 31 and the bore 25. The valve guide member 31 described in more detail.

alsace@ n is provided with an axial bore extending therethrough in which a reciprocable spool valve member 42, hereinafter called the control valve, is mounted for reciprocation, said control valve having end bearing lands 43 and 44 provided with peripheral grooves housing gaskets 4S and i6 respectively andrwith intermediate lands 47 and 4S effective to control fluid tlow. The portions of the control valve-42 between the various lands is, of course, of reduced diameter. The land-44 extends slightly beyond the end of the valve guidel and the exposed portion of the control valve member is provided with a peripheral groove Vin which a snapring 47 is seated to limit the extent of movement of the valve member 42 to the left as viewed in FIG. 4. The land d3 of the control valve 42 extends beyond the flangedtend of the valve guide member and the exposed portion thereof is provided with a T-shaped head 48 formed by parallel transverse slots and said T- Vshaped head is engaged by a corresponding or complementary slot formed in the end of the operating member 35. The outer end of the control valve 42 is provided with a shallow countersunk portion and vthe shank t9 ofthe member` isprovided with a ball Sil in the axial line thereof pressed outwardly by a compression spring 51 contained in an axial socket in the shank 49 displacably engaging the counterbore in the end of the valve member and thus tending to hold the operating member 35 in axial alignment with the control valve.

At` its outer end, the operating member 35 terminates in a yokeportion 52 through which a clevis bolt 53 extends, said bolt externally -of the yoke 52 clamping collars 54, 54 against the outer faces of the yoke and said collars extend through slightly elongated slotslSS formed in upstanding arms 56, 56 formed integrally with the base member 1. The bolt 53 is secured by a nut 57 and between the inner facesof the yoke 52 the bolt 53 is adapted to be connected to la suitable operating instrumentality which may be either a manually operable means as, for example, the hand lever L, a driven component of a servomechanism, or `a combination of both. Because this valve may be operated manually or by other control mechanism, it has been designated as a control valve to distinguish itfrom the various check valves in the apparatus.

Between the gaskets 36 and 37 thereon, the valve guide member 31 is provided with a peripheral groove 5d from the bottom of which one or more radially extending ports 59 extend therethrough to the interior of the valve 'guide memberg'said peripheral groove communicating with a fluid passage 6i) formed inthe member 1 and which communicates with a bore 61 formed in the member 1 and extends parallel to the bore 25; said bore 61 housing certain check valve devices hereinafter to be At its outer end, the passage 60 is closed by a screw 62 and at its opposite end it communicates with a passage 63 extending parallel to `and Ispaced from the bore 25 and the cylinder 2, said passage 63 at the end of the member 1 engaged by the lock nut'Z?r is closed by a screw 64.

Between the peripheral gaskets 37 and 38, the valve guide member 31 is provided with a peripheral groove 65 which mates with a shallow peripheral groove 66 on the inner face of thebore 25 and which at diametrically opposite points has ports 67 extending therethrough to the interior of the valve guide memberl. The body 1 is provided with a bore or fluid passage 68 extending at right angles to the bore 25 and at one side thereof and which is tangential to a Vbore of slightly smaller diameter than the bore 25 whereby' itintersects the bore 25 and particularly the peripheral groove 66 formed therein as best shown in FIG. 6. At its outer end the passage 63 is closed lby a screw 69 and at its other end it communicates with a boreor passage 70 spaced from and extending parallel to the bore 25 and the cylinder 2, said passage 79 being at the opposite side of the body member 1 from the bore 63 and terminating at the end d of the body 1 from which the piston rod 4 projects and being closed at said end by a plug screw 71. A passage 72 extends between this outer end of the passage 7@ and the end of the cylinder 2 through which the piston rod e projects.

Between the gaskets 3S and 39, the valve guide mer-nber 31 is provided with a peripheral groove 73 which mates with a complementary shallow groove '74 on the inner face of the bore 25 and ports '76, 76 extend through the valve guide member from the bottom of the groove 'i3 to the interior thereof. A fluid passage 77 closed at the outer side face of the body 1 by a plug screw 73 affords communication between the iluid cavity formed by the grooves 73 and 74, the bore 61 at a-point spaced from the channel 6@ and with a third bore 79 laterally offset from and extending parallel to the bores 2S and 61.

The bore 79 forms the bottom of a cavity for a relief valve mechanism and said bore is provided with a rst couhterbore 8h and a second slightly larger counterbore tt. Seated at the bottom of the counterbore Sti on the shoulder formed by the juncture of the said counterbore and the bore 79 -is the base of a stop member S2 having an axial bore 83 extending therethrough and further having a reduced diameter sleevelike portion S4 projecting toward the outer end of the body 1. Also seated in the counterbore 81 is the tubular valve cage member '35 having external gaskets S6 and S7 engaging the wall of the counterbore 89 and having an internal diameter tting over the reduced diameter portion of stop member 82. Between the portions thereof engaged by the gaskets 86 and 87, the counterbore is provided with a peripheral channel S3 which is intersected by a bore 89 extending from the bore or `channel 63 adjacent the end thereof closed by the screw 64, said channel 39 being closed at its outer end by a plug screw 9i). Slidably mounted within the valve cage member is a valve member 91 engaging the stop S2 and yieldingly urged to a rest position by a compression spring 92 reacting between the back end of the valve member 91 and the bottom of an axial bore 93 in a plug member 94 threadedly engaging the outer end of the counterbore 81 and having a gasket 95 disposed in a channel in the outer surface thereof which engages the counterbore 81. By adjustment of the plug screw 94 axially, the force exerted by the spring 92 on the valve member91 can be varied. The valve cage member 85 opposite the .channel 8S is provided with ports 96, 96 which extend through the valve cage adjacent to the stop engaging end of the valve member 91, the interior of the valve cage member having a peripheral groove 97 communicating with the ports 96, 96. Additionally, the pressure iluid inlet port 98 of the body i terminates in a Yfluid passage 99 which communicates both with the bore 61 and with the inner end of the counterbore 81 adjacent the outer end of the valve cage member S5; said outer end of the valve cage member having ports 100, 19!) extending therethrough whereby the pressure, if any, of inlet pressure fluid'trom the supply is conducted to the back end of the valve member 91 to supplement the bias imposed thereon by the spring 92.

Between the gaskets 39 and di?, the valve guide member Slis provided with a peripheral groove 101 which mates with a corresponding and complementary groove 102 on the inner face of the bore 25 and a uid passage 103 extends from the groove 1622 to the interior of the cylinder 2 at the end thereof adjacent the stuffing box 16. Ports 1%, 104iextend from the bottom of the groove 161 to the interior of the valve guide member 31.

Between the gaskets 4U' and 41, the valve guide member 31 is provided with a peripheral groove 195 which mates with a shallow complementary groove 1% formed in the wall of the bore 25 and ports 107, 197 extend through the valve guide member from the bottom of the groove to the interior thereof. A bore 16S (see FIG. 8) affords communication between the channel or cavity formed by the grooves 1555 and 166 with the bore or passageway 63.

The bore 61 extends parallel to the bore 2S at the side thereof remote from the cylinder 2 and extends from end to end of the body member 1. At the end of said body member remote from the inlet port 98, the bore is reduced in diameter to receive a plug 1119 having a gasket 111i seated in the groove therein said plug having a head portion 111 engaging the shoulder formed by the juncture of the bore 61 and the smaller diameter portion in which the plug 109 is located. The outlet or exhaust port 112 communicates with the bore 61 adjacent the end or head 111 of the plug. Disposed in the bore 61 opposite the juncture of the outlet port 112 thereof is a valve cage member 113 having a series of longitudinal slots 11d, 11d` on the outer surface thereof and having ports 115 affording communication between the bottoms of the slots 111i and an axial bore 11o in the valve cage. The end of said valve cage remote from the plug 1d@ is counterbored to receive a check valve member 117 and a spring 11S reacting between the bottom of the bore 116 and the valve member 117 holds this valve member yieldingly seated on the end of a valve seat member 119 said valve member having an axial bore 121B extending therethrough and terminating at the end thereof remote from the valve 117 in a reduced diameter portion 121 disposed opposite a eripheral groove 122 formed in the bore 61 and communicating with the fluid passage 6G. The valve seat member 119 between its ends is provided with a peripheral groove housing a gasket 122 engaging the wall of the bore 61. Ports 123 extend between the bottom of the reduced diameter portion of the valve seat member and the axial bore 12@ thereof.

The end ot the valve seat member 119 remote from the plug 109 is engaged by the end of a second valve seat member 124 having an axial bore 125 extending therethrough further having a peripheral gasket 126 engaging the wall of the bore 61.

Next disposed in the bore 51 and engaging the end 0f a valve seat member 124 is a double ended valve cage 127 having a series of longitudinally extending grooves 123 on its outer surface. This valve cage member has an axial opening extending therethrough and comprising a relatively wide and shallow counterbore 129 at the end thereof adjacent the valve seat member 123 housing a valve element 131B yieldingly pressed against the valve seat member 123 by a spring 131 housed within a second counterbore 132 and abutting against a shoulder formed by a further reduced diameter bore 133 at the midlength of this valve cage member. Ports 134 extend through the wail of the member into the counterbore 132. The opposite end of the valve cage member is a mirror image duplicate of the end thereof just described and comprises a iirst counterbore 135 housing a valve element 136 yieldingly pressed against a valve seat member 137 by a spring 13S housed in a second counterbore 139 and seated against a shoulder formed by the juncture of the counterbore 139 with the intermediate bore 133. Qpposite the midlength of the valve cage member 127 the bore 61 is provided with a peripheral groove 1411 affording communication between all of the longitudinal grooves 12B; said groove 141 also communicating with the iiuid passage 77.

The valve seat member 137 is provided with a peripheral groove housing a gasket 142 engaging the side walls of the bore 61 and said valve seat member is further provided with an axial bore 143 extending therethrough. `The end of the valve seat member 137 remote from the valve 136 is engaged by a screen 145 which, in turn, is engaged by the end of a closure nut 146 threadedly engaging an enlarged internally threaded counterbored portion 1417 at the outer end of the bore 61; said nut having a plug por-tion closely fitting the bore 61 and provided with a gasket means 148. The inner end of the plug 146 is reduced in diameter and is provided with a series of radial slots 14@ which are disposed opposite a shallow groove 150 formed l'normal usage with hydraulic pressure applied and as those parts are positioned when the control valve 42 is in its neutral position. 1t will be noted that the adjacent ends of the valve lands 47 and i8 are spacexl apart a distance which is slightly greater than the distance between the adjacent edges of the ports 67 and 104 with which those lands cooperate, wherefore, when this valve member is centered, both ports will be slightly open.

Assuming iirst a load on lthe unit tending to move the yoke 23 toward the eye bolt 14, the tluid in the right hand end of the cylinder will tend to be expelled out of the port 11M. Assuming that this load is capable of moving the body 1 slightly to the right relative tothe control valve member i2 which, it will be assumed, is held stationary until the collars 54, 54 contact an end of the slots 55, 55, the port 1M will be slightly further opened due to the movement of the body 1 relative to the control valve 42.

The pressure on the fluid in the right hand end of the cylinder will of course extend to the iluid surrounding the f control valve d2 between the lands 47 and 48 and in the passage 77 including the fluid between the.A check valves 131i and 13rd, and since this body of fluid is trapped, the load is eifectually resisted. 1f the load on the unit should be in the opposite direction, the fluid in the left hand end of the cylinder through the port 67 and passage 77 will be similarly trapped to resist the load.

Next referring to FIG. 15, the unit is shown when intentional movement of the unit in a direction to move the yoke 23 and eye bolt 1K1 away from each other is desired or, as illustrated, movement of the body and cylinder to the right is to be achieved. The control valve l2 is caused to be moved to the right as far as lpermitted by the collars 54, 54 in which position the land 48 permits communication between the passages 77 and 103 and the land #i7 similarly permits communication between the passages 60 and 72 thus fluid passes from the inlet port 98 through check valve 136 to passage 77 and thence to the right hand end of the cylinder while expelled iluid from the left hand end of the cylinder flows into passage di) and thence through check valve 117 to outlet port 112; it being remembered that check valve 131i at this time is held closed both by its own spring and by the inlet pres'- sure. When the desired extent of relative movement between the cylinder and piston is achieved, the control valve 42 is caused to be returned to its neutral position and the unit is automatically locked at that position.

To cause opposite relative movement between the cylinder and piston, the controlvalv'e i2 is caused to be moved to the left as shown in FIG. 16. This causes the land i7 to interconnect the passages 72 and 77 and the land 43 simultaneously to interconnect passages 103 and 63, the latter being in communication with passage 60. Pressure duid will thus flow from inlet port 93 through check valve 13d and passages 77 and 72 to the left hand end of cylinder 2 causing the cylinder and body to move to the left with incident expulsion of fluid from the right hand end of the cylinder through passages 1113, 63 and 6l), past check valve 117 to outlet port 112; it being again noted that the imposition of inlet pressure on check valve 13@ forces the fluid to pass check valve 117.

' As before mentioned, when the desired extent of movement has been achieved, the control valve 42 is returned to neutral with resultant locking of the unit in the position to which it has been moved.

ToV provide a means for protecting the unit and the system with which the unit is connected -against damage from abnormal loads thereon, the relief valve 91 is incorporated in the body 1 to be subjected to load imposed pressures by having the end thereof disposed in communication with the passage 77. The fact that it is biased both by spring means and by inlet pressure has already beenA aisance noted. In the event that load imposed pressures develop to la greater than predetermined extent, the yielding lresponse of this relief valve will allow som-e of the iluid to escape into the passage 89. This will, of course, be accompanied by compensatingv movement of the body It and cylinder 2 to the left relative to the control valve i2 which is the same as intentionally causing that valve to be moved to the right as shown in FIG. 15 thus opening the port 67 into communication with the port 59 and allowing the escaped iiuid Ato pass therethrough to the left hand end of the cylinder 2. If the excess loading is in the opposite direc-tion, the valve 91 will similarly allow iluid to enter the passage S9 and thence to the passage 60 and through passage 63 and passage 163 to the right hand end of the cylinder 2. This compensatory action will, of course, be sensed by the pilot of the aircraft or by the operator of the machinery or other apparatus to which the unit is connected and suitable remedial action can be taken. Preferably, 'the spring 92 imposes a load on the valve 91 equal to the normal operating pressure of the system so that this valve will not yield to less than twice the system pressure when the system is subjected to normal operating pressure.

Next, assuming a failure of operating pressure at least to an extent incapable of unseating check valve 136` and referring again to FIG. 14 with the control valve d2 centered, it will be noted that check valves 13@ and 136, as above described, serve to lock the unit against movement in any position to which it may have been moved. If, under conditions of inadequate operating pressure, it is desired to achieve relative movement of the cylinder and piston, the control valve 42 is moved in the direction in which the cylinder is intended to be moved. Assuming that the control valve is moved to the right as shown in FIG. 15, the cylinder and` body can then be moved by suitable external means to the right with expulsion of fluid through passage 72` into passage 60. Since there is little, if any, inlet pressure, the resistance offered by the check valve 130 i-s less than that of check valve 117, wherefore, the expelled iluid will pass through check valve 130 into passage 77 and thence to the right hand end of cylinder 2 through passage 163. Upon return of the valve 42 to neutral position when the extent of movement of the cylinder desired has been achieved, the unit will be locked in the position to which it has been moved.

Correspondingly if under these conditions it is desired to move the cylinder and body to the left, the control valve 42 is moved to the left as shown in FIG. 16 and the desired relative movement of cylinder and piston thereafter achievedl by other means. Fluid will be expelled from the right hand end of the cylinder 2 through passages 103 and 63 to passage 60 and again, since check valve 130 now oifers less resistance than check valve 117, the fluid will pass check valve 130 into passage 77 and thence will enter the left hand end of cylinder Z through passage '72 until the control valve 42 is returned to neutral position to lock the unit.

It is particularly to be noted that neither the provision for overload relief nor for operation in the absence of operating pressure involves the loss of iluid from the unit and that consequently, under all conditions, the operative integrity of the unit is maintained so that at any relative position of the piston and cylinder, with the control valve in the neutral position, the unit is locked against further movement except insofar as abnormal loading may produce minor changes warning the pilot or other operator of the existence of an overload or under conditions where the supply pressure fails and that because of this self-locking feature, the unit serves at all times as a control for the mechanism to which it may be connected.

The illustrated embodiment of the invention shown in FlGS. 1 through 13 operates exactly in the manner discussed in the description of the operation of the device shown schematically in FIGS. 14, l5 and 16, the only difference being' the provision of the necessary structural elements to achieve the desired results. Accordingly, a description of the nature of operation of the said physical embodiment of the invention is deemed to be merely repetitious of the description of the mode of operation in connection with the schematic disclosure of FIGS. 14, l5 and 16.

While in the foregoing speciiication there has been disclosed and described a presently preferred embodiment of the invention, the invention is not to be deemed to be limited to the precise details of construction thus shown by way of example, and it will be understood that the invention includes as well all such changes and modifications in the parts and in the construction, cornbination and arrangement of parts as shall corne within the purview of the appended claims.

l claim:

1. A hydraulic actuator and control unit comprising a body having a cylinder, a piston reciprocable in said cylinder; said piston having piston rod means slidably engaging stuliing box means at both ends of said cylinder, means for attaching one end of said cylinder and one end of said piston to separate elements of mechanism to he given relative movement by said actuator, a hydraulic fluid inlet port in said body, a hydraulic iluid outlet port in said body, a control valve means in said body normally occupying a position in which both ends of said cylinder are subjected to equal pressures and said valve means being operable in opposite directions from said normal position to admit pressure fluid from said inlet port to a selected end of said cylinder and simultaneously connecting the opposite end of said cylinder with said outlet port, means limiting the extent of movement of said control valve relative to said body, a valve seat in said body, a valve element responsive to ditlerential pressures normally engaging said valve seat; one side of said valve element being exposed to the pressure in said inlet port and said inlet pressure tending to hold said valve element on said seat and the other side of said valve element being exposed to pressure of fluid being discharged from either end of said cylinder, and spring means constantly imposing a bias in addition to that of the inlet pressure to said one side of said valve element whereby said valve element is yieldingly maintained on said seat to prevent iluid iiow through said valve seat in a direction toward said one side of said valve element unless it is unseated by pressure of fluid issuing from said cylinder in response to abnormal loads on the elements of a mechanism connected to said actuator sucient to effect movement of said body relative to said control valve with resultant` creation of pressures on said other side of said valve element which are greater than the combined load imposed on said one end thereof by said spring means and the inlet pressure.

2. A combined actuator and control unit as claimed in claim l in which the pressure imposed on said one side of said valve element is isolated from the rest of the valve element by a cage means in which said valve element is movable toward and away from said valve seat.

3. A hydraulic actuator and control unit comprising a body having a cylinder, a piston reciprocable in said cylinder; said piston having piston rod means slidably engaging stuiling box means at both ends of said cylinder, means for attaching one end of said cylinder and one end of said piston to separate elements of mechanism to be given relative movement by said actuator, a hydraulic fluid inlet port in said body, a hydraulic fluid outlet port in said body, a control valve means in said body normally occupying a position in which both` ends of said cylinder are subjected to equal pressures and said valve vmeans being operable in opposite directions from said normal position to admit pressure fluid from said inlet port to a selected end of said cylinder and simultaneously connecting the opposite end of said cylinder with said outlet port, means limiting the extent of movement of said control valve relative to said body and means contained within said body automatically operative to relieve abnormal pressures developed at either side of said piston in said cylinder deriving from overloads on the elements of a mechanism to which said cylinder and piston are connected with preservation of the Operative integrity of the cylinder and piston, the control valve means and the tluid contained therewithin.

4. A hydraulic actuator and control unit comprising a body having a cylinder, a piston reciprocable in said cylinder; said piston having a piston rod means slidably engaging stufiing box means at both ends of said cylinder, means for attaching one end of said cylinder and one end of said piston to separate elements of mechanism to be given relative movement by said actuator, a hydraulic uid inlet port in said body, a hydraulic fluid outlet port in said body, a control valve means in said body normally occupying a position in which both ends of said cylinder are subjected to equal pressures and said valve means being operable in the presence of an inlet pressure in excess of a predetermined value to admit pressure iluid from said inlet port to a selected end of said cylinder and simultaneously connecting the opposite end of said cylinder with said outlet port, means limiting the extent of movement of said control valve relative to said body and check valve devices contained within said body constantly effective to retain all iiuid in said unit at any time during which the system pressure drops and remains below said predetermined value.

5. A hydraulic actuator and control unit comprising a body having a cylinder, a piston reciprocable in said cylinder; said piston having piston rod means slidably engaging stuiting box means at both ends of said cylinder, means for attaching one end of said cylinder and one end of said piston to separate elements of a mechanism to be given relative movement by said actuator, a hydraulic riuid inlet port in said body, a hydraulic iiuid outlet port in said body, a control valve means in said body normally occupying a position in which both ends of said cylinder are subjected to equal pressures and said valve means being operable in the presence of an inlet pressure in excess of a predetermined value to admit pressure duid from said inlet port to a selected end of said cylinder and simultaneously connecting the opposite end of said cylinder with said outlet port, means limiting the extent of movement of said control valve relative to said body means contained Within said body automatically operative to relieve abnormal pressures developed at either side of said piston in said cylinder deriving from overloads on the elements of mechanism to which said cylinder and piston are connected, and devices contained within said body constantlly eiective to retain all uid in said unit at any time during which the system pressure drops and remains beloW a predetermined value; each of said pressure relieving means and said unit isolating devices serving additionally to preserve the operative integrity of said unit under all conditions of system pressure drop and overload relief action.

6. A hydraulic actuator and control unit comprising a body having a cylinder, a piston reciprocable in said cylinder; said piston having piston rod means slidably engaging stuiiing box means at both ends of said cylinder, means for attaching one end of said cylinder and one end of said piston to separate elements of a mechanism to be given relative movement by said actuator, a hydraulic uid inlet port in said body, a hydraulic iiuid outlet port in said body, a control valve means in said body normally occupying a position in which both ends ot said cylinder are subjected to equal pressures and said valve means being operable in opposite directions from said normal position to admit pressure tluid from said inlet port to a selected end of said cylinder and simultaneously connecting the opposite end of said cylinder with said outlet port, means limiting the extent of movement of said control valve relative to said body and differential pressure responsive valve means in said body comprising a Valve element normally seated on a valve seat to prevent fluid iloW therethrough, means for yieldingly maintaining said valve seated comprising an end of said valve subjected to the pressure in said inlet port and a compression spring engaging said end of said valve, iiuid passage means extending through said body from both ends of said cylinder past said control valve means and extending to the side of said valve seat opposite the side engaged by said valve element, and iluid passage means extending through said body from the side of said valve seat engaged by said valve element and atording communication with the end of said cylinder opposite an end subjected to overload and consequent abnormal pressure whereby fiuid forced from one end of said cylinder by overload on the elements of mechanism connected to the cylinder and piston is transferred to the opposite end of the cylinder While preserving the operative integrity of the unit.

7. A hydraulic actuator and control unit comprising a body having a cylinder, a piston reciprocable in said cylinder; said piston having piston rod means slidably engaging stuiiing box means at both ends of said cylinder, means for attaching one end of said cylinder and one end of said piston to separate elements of a mechanism to be given relative movement by said actuator, a hydraulic tluid inlet port in said body, a hydraulic iiuid outlet port in said body, a control valve means in said body normally occupying a position in which both ends of said cylinder are subjected to equal pressures and said valve means being operable in opposite directions from said normal position to admit pressure fluid from said inlet port to a selected end of said cylinder and simultaneously connecting the opposite end of said cylinder with said outlet port, means limiting the extent of movement of said control valve relative to said body; said control valve means comprising a spool type valve element mounted for reciprocable movement in a guide member carried by said body, said guide member having iiuid passageways extending therethrough from the portion in which said valve element is reciprocable to the exterior surface thereof and communicating with other passages in said body; said other passages including a lirst passage extending to one end of said cylinder, a second passage extending to the opposite end of said cylinder, a third passage extending to said inlet port, and a fourth passage extending to said outlet port, a spring biased check valve in said third passage effective to prevent liuid dow into said inlet port from said third passage, a spring biased check valve in said fourth passage effective to prevent iiuid oW from said outlet port into said fourth passage, a iifth passage extending between said third and fourth passages and disposed upstream of Said check valve in said fourth passage and downstream ci said check valve in said third passage, and a spring biased check valve in said fifth passage effective to prevent fluid otv therethrough from said third passage to said fourth passage.

8. A combined actuator and control unit as claimed in claim 7 in which the spring bias on said check valve in said fourth passage is greater than the spring bias on said check valve in said other passage.

9. A hydraulic actuator and control unit comprising a body having a cylinder, a piston reciprocable in said cylinder; said piston having piston rod means slidably engaging stufling box means at both ends of said cylinder, means for attaching one end of said cylinder and one end of said piston to separate elements of a mechanism to be iven relative movement by said actuator, a hydraulic fluid inlet port in said body, a hydraulic fluid outlet port in said body, a control valve means in said body normally occupying a position in which both ends of said cylinder are subjected to equal pressures and said ll valve means being operable in opposite directions from said normal position to admit pressure fluid from said inlet port to a selected end of said cylinder and simultaneously connecting the opposite end of said cylinder with said outlet port, means limiting the extent of movement of said control valve relative to said body; said control valve means comprising a spool type valve element mounted for reciprocable movement in a guide member carried by said body, said guide member having uid passageways extending therethrough from the portion in which said valve element is reciprocable to the exterior surface thereof and communicating with other passages in said body', said other passages including a first passage extending to one end of said cylinder, a second passage extending to the opposite end of said cylinder, a third passage extending to said inlet port, and a fourth passage extending to said outlet port, a spring biased check valve in said third passage effective to prevent uid ow into said inlet port from said third passage, a spring biased check valve in said fourth passage effective to prevent duid flow from said outlet port into said fourth passage, a fifth passage extending between said third and fourth passages and disposed upstream of said check valve in said fourth passage and downstream of said check valve in said third passage, and a spring biased check valve in said fth passage eiective to prevent fluid loW therethrough from said third passage to said fourth passage; a valve seat in said body, a valve element responsive to diierental pressures normally engaging said valve seat; one side of said valve element being exposed to the pressure in said inlet port and said inlet pressure tending to hold said valve element on said seat and the other side of said valve element being exposed to pressure of fluid being discharged from either end of said cylinder, and spring means constantly imposing a bias in addition to that of the inlet pressure to said one-end of said valve element whereby said valve element is yieldingly maintained on said seat to prevent uid oW through said valve seat in a direction toward said one end of said valve element unless it is unseated by pressure of iluid issuing from said cylinder in response to abnormal loads on the elements of mechanism connected to said actuator suicient to effect movement of said body relative to said control valve with resultant creation of pressures on said other side of said valve element which are greater than the combined load imposed on said one end thereof by said spring means and the inlet pressure.

References Cited by the Examiner UNITED STATES PATENTS 2,395,671 2/46 Kleinhans et al.

2,566,273 8/ 51 Westbury.

2,741,895 8/56 Howath 121-38 X 2,958,282 l/61 Hayman et al. 121-38 FRED E. ENGELTHALER, Primary Examiner.

KARL I. ALBRECHT, Examiner. 

1. A HYDRAULIC ACTUATOR AND CONTROL UNIT COMPRISING A BODY HAVING A CYLINDER, A PISTON RECIPROCABLE IN SAID CYLINDER; SAID PISTON HAVING PISTON ROD MEANS SLIDABLY ENGAGING STUFFING BOX MEANS AT BOTH ENDS OF SAID CYLINDER, MEANS FOR ATTACHING ONE END OF SAID CYLINDER AND ONE END OF SAID PISTON TO SEPARATE ELEMENTS OF MECHANISM TO BE GIVEN RELATIVE MOVEMENT BY SAID ACTUATOR, A HYDRAULIC FLUID INLET PORT IN SAID BODY, A HYDRAULIC FLUID OUTLET PORT IN SAID BODY, A CONTROL VALVE MEANS IN SAID BODY NORMALLY OCCUPYING A POSITION IN WHICH BOTH ENDS OF SAID CYLINDER ARE SUBJECTED TO EQUAL PRESSURES AND SAID VALVE MEANS BEING OPERABLE IN OPPOSITE DIRECTIONS FROM SAID NORMAL POSITION TO ADMIT PRESSURE FLUID FROM SAID INLET PORT TO A SELECTED END OF SAID CYLINDER AND SIMULTANEOUSLY CONNECTING THE OPPOSITE END OF SAID CYLINDER WITH SAID OUTLET PORT, MEANS LIMITING THE EXTENT OF MOVEMENT OF SAID CONTROL VALVE REALTIVE TO SAID BODY, A VALVE SEAT IN SAID BODY, A VALVE ELEMENT RESPONSIVE TO DIFFERENTIAL PRESSURES NORMALLY ENGAGING SAID VALVE SEAT; ONE SIDE OF SAID VALVE ELEMENT BEING EXPOSED TO THE PRESSURE IN SAID INLET PORT AND SAID INLET PRESSURE TENDING TO HOLD SAID VALVE ELEMENT ON SAID SEAT AND THE OTHER SIDE OF SAID VALVE ELEMENT BEING EXPOSED TO PRESSURE OF FLUID BEING DISCHARGED FROM EITHER END OF SAID CYLINDER, AND SPRING MEANS CONSTANTLY IMPOSING A BIAS IN ADDITION TO THAT OF THE INLET PRESSURE TO SAID ONE SIDE OF SAID VALVE ELEMENT WHEREBY SAID VALVE ELEMENT IS YIELDINGLY MAINTAINED ON SAID SEAT TO PREVENT FLUID FLOW THROUGH SAID VALVE SEAT IN A DIRECTION TOWARD SAID ONE SIDE OF SAID VALVE ELEMENT UNLESS IT IS UNSEATED BY PRESSURE OF FLUID ISSUING FROM SAID CYLINDER IN RESPONSE TO ABNORMAL LOADS ON THE ELEMENTS OF A MECHANISM CONNECTED TO SAID ACTUATOR SUFFICIENT TO EFFECT MOVEMENT OF SAID BODY RELATIVE TO SAID CONTROL VALVE WITH RESULTANT CREATION OF PRESSURES ON SAID OTHER SIDE OF SAID VALVE ELEMENT WHICH ARE GREATER THAN THE COMBINED LOAD IMPOSED ON SAID ONE END THEREOF BY SAID SPRING MEANS AND THE INLET PRESSURE. 